Minimally invasive surgery is surgery performed with only a small incision or no incision at all and is typically performed with an endoscope, bronchoscope, laparoscope, or like instrument.
In a bronchoscopic procedure, for example, a bronchoscope is inserted through the nose or mouth of the patient, advanced through the trachea and into a desired airway. The surgery may then be performed through the working lumen of the bronchoscope. A light source and camera at the tip of the bronchoscope enables the physician to observe the airway wall in real time. A skilled physician can identify his location along the airway and navigate to the desired location along the airway wall.
It is often desirable, however, to supplement endoscopic visualization with radiological guidance (e.g., by taking real time X-ray images of the region with a fluoroscope). In certain procedures radiologic guidance is necessary.
In a transbronchial needle aspiration (TBNA) procedure, for example, a long flexible catheter comprising a needle at the tip is advanced through the working lumen of the bronchoscope to the target site. The needle is then advanced through the airway wall outside of view of the bronchoscope to aspirate a sample of tissue. It is highly desirable or necessary to have fluoroscopy or an alternative means to view and track the needle once it is outside of view of the bronchoscope.
Various tracking approaches are available. One approach is described in US Patent Publication No. 2003/0181809 to Hall et al. (hereinafter referred to as “the Hall Publication”). The Hall Publication describes a method of visualizing a surgical instrument that has been introduced into an area of examination within a patient, in particular a catheter that is used during a cardiological examination or treatment, comprising the following steps: using a 3D image data set of the area of examination and generating a 3D reconstructed image of the area of examination, taking at least one 2D X-ray image of the area of examination in which the instrument is visualized, registering the 3D reconstructed image relative to the 2D X-ray image, and visualizing the 3D reconstructed image and superimposing the 2D X-ray image over the 3D reconstructed image on a monitor.
Another approach to track the surgical devices with fluoroscopic visualization is described in international patent application serial number PCT/US12/37026, filed May 9, 2012.
The performance of such visualization and tracking approaches are dependent on the performance and accuracy of the fluoroscopic projection images. The fluoroscope must therefore be properly calibrated. Stated alternatively, an un-calibrated camera can introduce errors and thwart tracking and registration performance.
Calibration data may be obtained off-line and be calculated by acquiring multiple fluoroscopic images of radio-opaque markers to determine such data as the focal lengths and camera center of fluoroscopic camera, and a representation of the deformation pattern wherein a checkerboard pattern appears curved when viewed in the fluoroscope, and variation of these parameters as the fluoroscope is rotated throughout its range of motion. The calibration factors can be specific to each fluoroscope. Examples of calibrating techniques include those described in References 2-5, and 8, listed below. However, off-line measurement can be slow, inconvenient, and susceptible human error.
A method and system to more accurately, more conveniently, and more rapidly determine the calibration parameters is desired.